1. Field of the Invention
The present invention relates to an electrochemical element for carrying out energy conversion between a chemical energy and an electric energy using a solid electrolyte.
2. Description of Related Art
FIG. 9 is a block diagram of an electrochemical element disclosed in, for example, the Japanese Patent Publication (unexamined) No. 63343/1994 as an energy conversion element using a solid electrolyte. Referring to FIG. 9, a first electrode 2 is formed on one side of a solid electrolyte membrane 1 possessing hydrogen ion conductivity, and a second electrode 3 is formed on the other side of the solid electrolyte membrane 1. Further, the solid electrolyte membrane 1 is, for example, Nafion-117 (trademark) produced by Du Pont de Nemours and Co. The first electrode 2 is a mixed layer of a platinum-plated stainless fiber having a power-feeding performance, an expand metal of titanium, a platinum black functioning as a catalyst, and solid electrolyte components. Further, the second electrode 3 is a mixed layer of a platinum-plated stainless fiber having a power-feeding performance, a platinum black functioning as a catalyst and, solid electrolyte components. Numeral 4 designates a direct current power supply. A plus side of the direct current power supply 4 is connected to the first electrode 2, and a minus side thereof is connected to the second electrode 3.
In the above-mentioned construction, when establishing the first electrode 2 as a high water activity side space (I) on the side of a high humidity, and the second electrode 3 as a low water activity side space (II) on the side of a low humidity, a reaction expressed by the following formula (1) takes place on the side of the first electrode 2, and a reaction expressed by a formula (2) takes place on the side of the second electrode 3:H2O→2H++(1/2)O2+2e−  (1)2H++(1/2)O2+2e−→H2O  (2)That is, decomposition of water takes place at the first electrode 2, while generation of water takes place at the second electrode 3. Accordingly, water moves from the high water activity side space (I) on the side of high humidity to the low waver activity space (II) on the side of low humidity.
Even when the reactions expressed by the mentioned formulas (1) and (2) proceed to the extent that humidity in a space adjacent to the first electrode 2 becomes lower than that in a space adjacent to the second electrode 3, the conditions can be kept. In addition, difference in humidity between the high water activity side space (I) and the low water activity side space (II) can be controlled by application of a voltage. Thus, the humidity control in each space (I) or (II) can be conducted.
In the mentioned conventional electrochemical element, however, an output voltage in the case of collecting an electronic energy utilizing the difference in water activity between the two electrodes 2 and 3 is so low as to be several mv, even if humidity on one surface is set to a level of 100% and humidity on the other surface set to a level of 10% thereby establishing an activity difference by ten times between the two electrodes 2 and 3. Accordingly, a problem exists in that it is difficult to elevate the output voltage.